Evaluation of Countermeasures for Hydraulic Loading on Bridges

Stream-crossing bridges are critical components of the surface transportation system, allowing for the safe and efficient movement of people and goods. However, these bridges may be subjected to extreme hydraulic loading during flood events. To ensure the longevity and functionality of bridges, it is important to evaluate and implement effective countermeasures against hydraulic failure. This study used computational fluid dynamics modeling to quantify the magnitude of hydraulic loading on typical I-girder, box beam, and slab beam bridges in Texas under extreme flow conditions and debris damming and evaluated the efficacy of existing design guidelines for countermeasures (i.e., shear keys and earwalls) meant to resist shear failure of bridges during flood events. Results indicate that the drag force induced by hydraulic loading during a range of annual exceedance probability events (2%-0.2%) can exceed the capacity of a shear key or an earwall, especially for bridges with greater flow blockage area. Flat plate debris damming on the upstream side of the bridge causes a 46% increase in the drag force compared to the no-debris condition, resulting in a force 2.3 times the shear capacity of the shear key. For the cases where the interface shear strength is not sufficient, several approaches are recommended to increase the interface shear capacity: (1) increase the size and/or quantity of the interface shear reinforcement; (2) increase the number of shear keys; and/or (3) increase the length of the bent cap hence the length of the earwall. Findings from this work can inform the development of more robust design criteria for countermeasures to reduce the risk of hydraulic-induced failures at stream-crossing bridges.